C 字符输入输出和输入确认

//一个菜单程序
#include<stdio.h>
char get_choice(void);
char get_first(void);
int get_int(void);
void count(void);
int main(void)
{
    int choice;
    void count(void);

    while((choice=get_choice())!=‘q‘)
    {
        switch(choice)
        {
        case ‘a‘:printf("Buy low,sell high.\n");
            break;
        case ‘b‘:putchar(‘\a‘);
            break;
        case ‘c‘:count();
            break;
        default:printf("program error！\n");
            break;
        }
    }
    printf("Bye.\n");
    return 0;
}

void count(void)
{
    int n,i;
    printf("count how far? Enter an integer:\n");
    n=get_int();
    for(i=1;i<=n;i++)
        printf("%d\n",i);
    while(getchar()!=‘\n‘)
        continue;
}

char get_choice(void)
{
    int ch;
    printf("Enter the letter your choice:\n");
    printf("a.advice            b.bell\n");
    printf("c.count             q.quit\n");
    ch=get_first();
    while((ch<‘a‘||ch>‘c‘)&&ch!=‘q‘)
    {
        printf("please respond with a,b,c,or q.\n");
        ch=get_first();
    }
    return ch;
}

char get_first(void)
{
    int ch;
    ch=getchar();
    while(getchar()!=‘\n‘)
        continue;
    return ch;
}

int get_int(void)
{
    int input;
    char ch;

    while(scanf("%d",&input)!=1)
    {
        while((ch=getchar())!=‘\n‘)
            putchar(ch);//剔除错误的输入
        printf("is not an integer.\n");
        printf("please enter an integer value,such as 25,-178,or 3:");
    }
    return input;
}

//重复输入
//putchar()函数和getchar()的使用
#include<stdio.h>
int main(void)
{
    char ch;

    while((ch=getchar())!=‘#‘)
        putchar(ch);
    return 0;
}

//重复输入，知道文件的结尾
//使用EOF来标记文件的结尾   ctral+z
//每次按下回车键，处理缓冲区中存储的字符，并且打印一行副本。
#include<stdio.h>
int main(void)
{
    char ch;

    while((ch=getchar())!=EOF)
        putchar(ch);
    return 0;
}

//打开一个文件并显示其内容
#include<stdio.h>
#include<stdlib.h>//为了适应exit()
int main(void)
{
    int ch;
    FILE*fp;
    char fname[50];//用于存放文件名

    printf("Enter the name of the file:");
    scanf("%s",fname);
    fp=fopen(fname,"r");//打开文件以供读取
    if(fp==NULL)//尝试打开文件失败
    {
        printf("Failed to open file.Bye\n");
        exit(1);//终止程序
    }
    //getc(fp)从打开的文件中获取一个字符
    while((ch=getc(fp))!=EOF)
        putchar(ch);
    fclose(fp);  //关闭文件
    return 0;
}

//猜数游戏
#include<stdio.h>
int main(void)
/*{
    int guess=1;
    printf("Pick an integer from 1 to 100.I will try to guess it.\n");
    printf("Respond with a y if my guess is right and with \n");
    printf("an n if it is wrong.\n");
    printf("UH....is your number %d?\n",guess);
    while((getchar()!=‘y‘))             //获取用户响应并和y比较
        printf("Well,then,is it %d?\n",++guess);
    printf("I kenw I could do it!\n");
    return 0;
}*/
//
/*{
    int guess=1;
    printf("Pick an integer from 1 to 100.I will try to guess it.\n");
    printf("Respond with a y if my guess is right and with \n");
    printf("an n if it is wrong.\n");
    printf("UH....is your number %d?\n",guess);
    while((getchar()!=‘y‘))             //获取用户响应并和y比较
    {
        printf("Well,then,is it %d?\n",++guess);
        while(getchar()!=‘\n‘)
            continue;
    }
    printf("I kenw I could do it!\n");
    return 0;
}*/
//使用一个if语句来筛选掉其他响应
{
    char Response;//添加一个变量来存储响应！！！
    int guess=1;
    printf("Pick an integer from 1 to 100.I will try to guess it.\n");
    printf("Respond with a y if my guess is right and with \n");
    printf("an n if it is wrong.\n");
    printf("UH....is your number %d?\n",guess);
    //请注意，在修改的时候while判断语句也要改把值赋给变量Response
    while((Response=getchar())!=‘y‘)             //获取用户响应并和y比较
    {
        if(Response==‘n‘)               //使用一个if语句
            printf("Well,then,is it %d?\n",++guess);
        else
            printf("sorry,I understand only y or n.\n");//添加说明语句
        while(getchar()!=‘\n‘)
            continue;
    }
    printf("I kenw I could do it!\n");
    return 0;
}

//一个关于I/O问题的程序
//完成第一次打印染污后，程序提示输入第二组数据，可是在还没有做出响应之前程序就退出了，问题在哪里？
#include<stdio.h>
void display(char cr,int lines,int width);
int main(void)
{
    int ch;//要打印的字符
    int rows,cols;
    printf("Enter a character and two integers:\n");
    while((ch=getchar())!=‘\n‘)
    {
        scanf("%d%d",&rows,&cols);
        display(ch,rows,cols);//调用函数打印字符
        printf("Enter another character and two integers:\n");
        printf("Enter a newline to quit.\n");
    }
    printf("Bye!\n");
    return 0;
}

void display(char cr,int lines,int width)
{
    int row,col;//请注意这里的变量和主函数变量的区别
//用一个双重循环打印字符
    for(row=1;row<=lines;row++)
    {
        for(col=1;col<=width;col++)
            putchar(cr);
        putchar(‘\n‘);
    }
}
//scanf()函数将换行符留在了输入队列中，getchar()并不跳过换行符，所以在循环的下一个周期，
//在有机会输入第二组数据之前，这一换行符由getchar读取，然后赋值给ch，而ch为换行符则正是终止循环的条件
/*
#include<stdio.h>
void display(char cr,int lines,int width);
int main(void)
{
    int ch;//要打印的字符
    int rows,cols;
    printf("Enter a character and two integers:\n");
    while((ch=getchar())!=‘\n‘)
    {
        if(scanf("%d%d",&rows,&cols)!=2)//判断输入
            break;
        display(ch,rows,cols);//调用函数打印字符
        while(getchar()!=‘\n‘)//如果读取的是一个字符，则跳出
            continue;
        printf("Enter another character and two integers:\n");
        printf("Enter a newline to quit.\n");
    }
    printf("Bye!\n");
    return 0;
}

void display(char cr,int lines,int width)
{
    int row,col;
    for(row=1;row<=lines;row++)
    {
        for(col=1;col<=width;col++)
            putchar(cr);
        putchar(‘\n‘);//结束本行，开始新的一行
    }
}
*/

//输入确认
//在通常情况下，程序用户不总是遵循指令，在程序所期望的输入与实际获得的输入之间可能存在不匹配
#include<stdio.h>
#include<stdbool.h>
//确认输入了一个整数
int get_int(void)
//确认范围的上下界是否有效
bool bad_limits(int begin,int end,int low,int high);
//计算从a到b之间的整数的平方和
double sum_squares(int a,int b);
int main(void)
{
    const int MIN=-1000;
    const int MAX=+1000；
    int start;
    int stop;
    double answer;

    printf("This program computs the sum of the squares of"
        "integers in a range.\nThe lower bound should not"
        "be less than -1000 and\nthe upper bound should not"
        "be more than +1000.\nEnter the limits (enter 0 for"
        "both limits to quit):\nlower limit:");
    start=get_int();
    printf("upper  limit:");
    stop=get_int();
    while(shart!=0||stop!=0)
    {
        if(bad_limits(start,stop,MIN,MAX))
            printf("Please try again.\n");
        else
        {
            answer=sum_squares(stare,stop);
            printf("The sum of the squares of the integers from");
            printf("from %d to %d is %g\n",start,stop,answer);
        }
        printf("Enter the limits(enter 0 for both limits to quit):\n");
        printf("lower  limit：");
        start=get_int();
        printf("upper limit:");
        stop=get_int();
    }
    printf("Done!\n");
    return 0;
}

//使用get_int（）函数来获取值
int get_int(void)
{
    int input;
    char ch;

    while(scanf("%d",&input)!=1)//用while循环来处理值
    {
        while((ch=getchar())!=‘\n‘)
            putchar(ch);//剔除错误的输入
        printf("is not an integer.\n please enter an integer value,such as 25,-178,or 3:");
    }
    return input;
}

//程序核心部分，进行实际计算
double sum_squares(int a,int b)
{
    double total=0;
    int i;

    for(i=a;i<=b;i++)
        total+=i*i;
    return total;
}

//bad_limits（）函数来检查值的有效性
bool bad_limits(int begin,int end,int low,int high)
{
    bool not_good=false;
    if(begin>end)
    {
        printf("%d isn‘t smaller than %d.\n",begin,end);
        not_good=true;
    }
    if(begin<low||end<low)
    {
        printf("Values must be %d or greater.\n";low);
        not_good=true;
    }
    if(begin>high||end>high)
    {
        printf("Values must be %d or less.\n",high);
        not_good=true;
    }
    return not_good;
}